We propose to develop an area of chemistry based on cyclic olefins that are shielded on both faces by molecular chains of different lengths. Functional groups remote from the olefin and at allylic positions will be incorporated to probe their effect. The chemical behavior of these "protected" pi-bonds will be investigated including cis-trans isomerization, interaction with singlet oxygen and triplet oxygen, addition reactions, allylic site reactions, and transannular effects. Allene analogs will be pursued similarly. The geometric effects in these hidden pi-bond systems could reveal factors that play roles in enzyme-substrate complexation and, for allenic ketones specifically, in enzyme deactivation. The unique shielding and pi-bond distortion in the compounds may allow them to convert normal oxygen to singlet oxygen without being oxidized. Naturally occurring compounds with potent anti-tumor properties often contain transcycloolefinic pi-systems that are loosely covered by molecular segments, and these architectural features could influence biological activity.